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    Faster Plaster

    continued

    Company representative for CTS, Conrad Bigelow, explains that with Portland cement plaster, the building codes require a contractor to wait two days after application of the scratch coat (base layer) before applying the brown coat (second layer), and then seven more days before applying the top coat that gives stucco its final color and texture.

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    "This requires a contractor to return to the same job site at least three times to work on the same piece of wall, ties up scaffolding for almost half a month, and delays the progress of other trades that must wait until plastering is complete," says Bigelow.

    "The contractor also has to keep Portland cement plaster damp during the first 48 hours after applying both the scratch and brown coats," Bigelow adds. "Even with these steps, conventional stucco can develop shrinkage cracks that detract from a project's appearance and can result in costly callbacks for repair work."

    Proof is in the Plaster

    Unlike Portland cement, Eisenwall contains a special cement that cures completely in a matter of hours. This rapid-setting cement has been used for many years in other applications such as highway repairs. Bigelow says Eisenwall, however, is the first product using the cement specifically for plaster. It was tested extensively at the University of California, Los Angeles, before being brought to market.

    In addition to its strength development, Bigelow states that the special formulation of the plaster significantly reduces shrinkage cracking in plaster, resulting in fewer callbacks for repairs. It also produces a stronger, harder plaster that is more resistant to impact damage. The product is approved under an International Code Council (ICC) Evaluation Services Report and by the City of Los Angeles.

    One of Browne's first projects with the material, a 276-unit condominium and townhouse project in Milpitas, California, offers a side-by-side comparison of Portland cement and Eisenwall-based plasters.

    "We did the first part of the project with conventional Portland cement and experienced cracking right away," says Browne. "But when we switched to Eisenwall for the rest of the project, we noticed that cracking diminished tremendously."

    Learning New Applications

    Both Browne and Vera stress that the fast setting of the plaster requires better coordination of the crew to make sure the plaster doesn't harden before it can be applied and finished. With conventional concrete, one can start mixing plaster while the crew is still getting into position on the wall. But with this new material, everyone has to be in place and ready to go before mixing begins.

    Vera says that before, he had to wait over an hour before floating conventional plaster but with the new plaster he can start in approximately 20 minutes. Bigelow notes that a retarder is available for use on hot days and when it may be necessary to slow the reaction.

    Browne recommends that the crew be more diligent about how much they mix and apply and about washing out equipment during breaks. "Instead of my usual eight- to 10-person crew, I increase manpower to an 11- or 12- man crew, putting a couple of extra finish guys on the wall to keep up with the quick setting," he says.

    He also notes that using this product feels pretty much like working with conventional plaster, but that workers can only mix as much as can be finished in a short time. It requires coordination between the applicators spraying it on the wall and the workers coming along behind to screed and float it.

    Cost Versus Value

    The material costs a premium compared to ordinary Portland cement. But both contractors say it ends up making them money. Browne says the premium for the material is offset by indirect savings because equipment gets released sooner and he has to respond to fewer customer callbacks.

    Eisenwall, Browne says, also makes sense for smaller projects. "We used it on a model home that was on an accelerated schedule. The quicker the developer got the model open to the public, the quicker they could start getting sales."

    Both contractors say they have started using the cement on custom homes and small commercial projects to cut "windshield time" driving to and from job sites. "We use it on smaller projects where applying just one coat would not be a full day of work for a crew," Browne explains. "It allows us to do the first and second coat in the same day so we don't have to come back as often."

    The developer for whom the contractors work has run a cost/benefit analysis comparing the cost of materials to the savings in time. Because most of the total cost of stucco is in equipment and labor, not in materials, Eisenwall can be shown to be not dramatically more expensive than conventional stucco. The extra material cost is small relative to the total cost of construction.

    Discuss this article in the Architecture Forum...

    Michael Chusid, RA FCSI is an architect and a Fellow of the Construction Specifications Institute. His Los Angeles, California-based company Chusid Associates investigates and reports on the performance of new building products.

    A version of this article first appeared in the April 2006 issue of Walls & Ceilings. It is reprinted here with permission of the author.

     

    AW

    ArchWeek Image

    Spraying on quick-setting plaster.
    Photo: Michael Chusid

    ArchWeek Image

    Final stucco appearance.
    Photo: Michael Chusid

    ArchWeek Image

    Reducing the time scaffolding has to remain up is a major advantage of the new plaster.
    Photo: Michael Chusid

    ArchWeek Image

    Typical scratch coat.
    Photo: Michael Chusid

    ArchWeek Image

    Floating the newly applied plaster.
    Photo: Michael Chusid

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    Screeding the plaster surface.
    Photo: Michael Chusid

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    The completed housing with a stucco finish.
    Photo: Michael Chusid

    ArchWeek Image

    Cracking in Portland cement is a common problem largely avoided with the new plaster.
    Photo: Michael Chusid

     

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